Formation of carbon and semiconductor nanomaterials using molecular assemblies

ABSTRACT

The invention is directed to a method of forming carbon nanomaterials or semiconductor nanomaterials. The method comprises providing a substrate and attaching a molecular precursor to the substrate. The molecular precursor includes a surface binding group for attachment to the substrate and a binding group for attachment of metal-containing species. The metal-containing species is selected from a metal cation, metal compound, or metal or metal-oxide nanoparticle to form a metallized molecular precursor. The metallized molecular precursor is then subjected to a heat treatment to provide a catalytic site from which the carbon nanomaterials or semiconductor nanomaterials form. The heating of the metallized molecular precursor is conducted under conditions suitable for chemical vapor deposition of the carbon nanomaterials or semiconductor nanomaterials.

FIELD OF THE INVENTION

This invention relates to the use of molecular assemblies to direct theformation of carbon nanomaterials and semiconductor nanomaterials. Theinvention also relates to electronic and optoelectronic devices madewith carbon and semiconductor nanomaterials formed using the molecularassemblies.

BACKGROUND OF THE INVENTION

Carbon nanotubes, which can be either semiconducting or metallic, aretypically grown by arc discharge, laser ablation, or chemical vapordeposition. The nanotubes are then harvested from the growth surface forsubsequent use [H. Dai, Acc. Chem. Res. 35, 1035 (2002)]. Onceharvested, one remaining challenge is to position the carbonnanomaterials for use in devices, e.g., positioning them betweenelectrodes on selected substrates for electronic, optoelectronic orsensing applications. At the research level, individual carbon nanotubesare commonly brought into contact with electrodes by one of twotechniques. In one instance, the carbon nanotubes can be deposited ontosurfaces patterned with electrodes by spin-coating from a dispersion.However, only a small portion of the individual nanotubes actually comein contact with the electrodes. A second technique involves spin-coatingthe carbon nanotubes on a surface prior to electrode deposition. Theelectrodes are subsequently deposited with or without alignment of theelectrodes to the carbon nanotubes. The successful formation ofelectrical devices using carbon nanotubes is limited by serendipitouselectrode patterning or random nanotube deposition or if the electrodesare intentionally aligned to the nanotubes, to small numbers of devices.

At the research level the attractive performance of carbon nanotubes inelectronics and optoelectronics has been demonstrated, however,challenges remain with regard to scale-up of carbon nanotube deviceapplication and, in particular, in providing reliable contacts betweenthe nanotubes and the electrodes of the device. Routes that form carbonnanotubes in selected areas of a substrate avoiding exposure of thenanotubes to the potentially harmful solvents and oxidation processesused in harvesting, purification, and placement have recently been shownto form better performing devices. [J. Liu, S. Fan, H. Dai, M R S Bull.April, 244 (2004)].

Semiconductor nanowires are also typically grown by chemical vapordeposition and harvested from the growth surface for further use. Asemiconductor nanowire is a one-dimensional semiconductor. Thesemiconductor materials can be Group IV (such as Si, Ge, or an alloy),Group III-V (such as GaAs), Group II-VI (such as CdSe, CdS, ZnS), GroupIV-VI (such as PbSe) Thus, they face many of the same challenges inalignment and placement as carbon nanotubes for device applications [C.M. Lieber, MRS Bull. July, 286 (2003)]. Again, the process of harvestingand positioning nanowires on surfaces subjects the nanostructures topotentially harmful conditions. Methods for in-place growth of nanowiresare therefore preferred. [J. Li, C. Lu, B. Maynor, S. Huang, J. Liu,Chem. Mat. 16, 1633 (2004)].

Microfluidics has been used to orient and selectively deposit nanowiresand nanotubes on surfaces, but microfluidic channels are typicallylimited to micron widths by the fluidics of liquid flow at smalldimensions [H. Yuang, X. Duan, Q. Wei. C. Lieber, Science 291, 630(2001)]. Microfluidic approaches also would require the use ofsurfactants to disperse the nanowires and nanotubes in the deliverysolutions. The presence of surfactants, particularly for nanotubedeposition, can significantly affect the electronic properties of thenanotubes or nanowires unless the surfactants can be removed from theresulting nanomaterials. This approach requires the separate growth,harvesting, and placement of nanowires and nanotubes.

Ordered networks of suspended carbon nanotubes have been grown betweenregularly positioned silicon posts by patterning the catalysts on theposts and growing the nanotubes until they reach another post. [N.Franklin, H. Dai, Adv. Mat. 12, 890 (2000)]. In addition electric fieldshave been used to control the direction of nanotube growth by takingadvantage of their high polarizability [H. Dai, Acc. Chem. Res. 35, 1035(2002)]. In both instances, the nanotubes are suspended above thesubstrate surface. For many electronic and optoelectronic deviceapplications, the nanotube is preferably in contact with the substratesurface, e.g., the gate dielectric of a transistor for conductancemodulation.

Carbon nanotubes and semiconductor nanowires have been formed asvertical arrays on surfaces by spatially positioning catalytic sites.This approach typically provides a high density of at least locallyordered nanotubes and nanowires that extend perpendicular to thesubstrate surface. Although this approach may eliminate the need toharvest and place the nanotubes or nanowires in some applications,vertical arrays of these materials place severe constraints on devicegeometries and assumes that the growth surface is amenable to thedesired device structure.

To position the catalysts for nanotube or nanowire growth on surfaces,lithographic processing is commonly used. The catalysts used are eithermetal containing organic molecules or nanoparticles of metal or metaloxide [For examples see J. Liu, S. Fan, H. Dai, MRS Bulletin, April, 244(2004); S. Rosenblatt et. al., Nano Lett. 2, 869 (2002); and J. Hu, T.W. Odom, C. M. Lieber, Acc. Chem. Res. 32, 435 (1999)]. Lithographicpatterning of surfaces is useful across the substrate plane, but doesnot provide a route to pattern surfaces vertically.

SUMMARY OF THE INVENTION

The invention is directed to a method of forming carbon or semiconductornanomaterials. The method comprises providing a substrate and attachinga molecular precursor to the substrate, wherein the molecular precursorincludes a surface binding 0group for attachment to the substrate (a“head group”) and a binding group for attachment of metal-containingspecies (a “tail group”). The method includes complexing the bindinggroup with a metal-containing species, the metal-containing speciesselected from a metal cation, metal compound, or metal or metal-oxidenanoparticle to form a metallized molecular precursor. The method canfurther include complexing the metal-containing species with a ligandand additional metal-containing species that may be added repeatedly toincrease the amount of metal on the surface. The metallized molecularprecursor is then subjected to a heat treatment to provide a catalyticsite from which the carbon or semiconductor nanomaterials form.

The method of the invention can be used to make a transistor. In oneembodiment, the method comprises providing a first electrode and asecond electrode on a gate dielectric, and attaching a molecularprecursor to the first electrode, the second electrode or both the firstand the second electrodes. The molecular precursor includes a surfacebinding group for attachment to at least one electrode and a bindinggroup for attachment of metal-containing species. The method furtherincludes complexing the binding group for attachment of metal-containingspecies with a metal-containing species selected from a metal cation,metal compound, or metal or metal-oxide nanoparticle to form ametallized molecular precursor. The metallized molecular precursor isthen subjected to a heat treatment to provide a catalytic site fromwhich the carbon or semiconductor nanomaterials form.

In another embodiment, the method of making a transistor comprisesproviding at least two segments of a non-reactive layer on a gatedielectric, and providing a first electrode and a second electrode oneach of the at least two non-reactive layers. A molecular precursor isthen attached to the first electrode, the second electrode or both thefirst and the second electrodes, wherein the molecular precursorincludes a surface binding group for attachment to at least oneelectrode and a binding group for attachment of metal-containingspecies. The method further includes complexing the binding group forattachment of metal-containing species with a metal-containing speciesselected from a metal cation, metal compound, or metal or metal-oxidenanoparticle to form a metallized molecular precursor. The metallizedmolecular precursor is then subjected to a heat treatment to provide acatalytic site from which the carbon or semiconductor nanomaterials formabove the gate dielectric.

The invention is also directed to a method of making an electronicdevice structure. The method comprises providing a patterned electronicsurface selected from a patterned metal surface, patterned dielectricsurface or patterned semiconductor surface, and attaching a molecularprecursor to the patterned electronic surface. The molecular precursorincludes a surface binding group for attachment to the patternedelectronic surface and a binding group for attachment ofmetal-containing species. The method further includes complexing thebinding group for attachment of metal-containing species with ametal-containing species selected from a metal cation, metal compound,or metal or metal-oxide nanoparticle to form a metallized molecularprecursor. The metallized molecular precursor is then subjected to aheat treatment to provide a catalytic site on the patterned electronicsurface from which the carbon or semiconductor nanomaterials form.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will become apparentupon consideration of the following detailed description of theinvention when read in conjunction with the drawings, in which:

FIGS. 1( a) to 1(f) is a schematic for one method of making anelectronic device with a select orientation of carbon or semiconductornanomaterials;

FIG. 2 is a schematic for another method of making an electronic devicewith a select orientation of carbon or semiconductor nanomaterials;

FIG. 3 is a scanning electron micrograph of grown carbon nanotubes usinga process of the invention;

FIG. 4 is a scanning electron micrograph of grown carbon nanotubes usinganother process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a process to selectively positionnanomaterials, e.g., carbon nanotubes or semiconductor nanowires, usingan assembly of molecular precursors attached to a select substratesurface. By relying on various chemical interactions the molecularprecursors self-assemble on a selected surface. Exemplary surfaces onwhich to selectively grow carbon or semiconductor nanomaterials includedevice surfaces such as an electrode surface used in field-effecttransistors, light emitting diodes, photovoltaic devices and sensors.

The molecular assemblies formed in the process are used to selectivelyposition catalytic sites for carbon nanomaterial or semiconductornanomaterial formation in device structures. The chemical specificitiesof the molecular assemblies, and in particular, how the molecularassemblies selectively bind to surfaces, for example, the surfaces ofmetals, dielectrics and semiconductors, provide the necessary degree ofcontrol to the process. The assembled molecules act as sites to bindmetal cations, metal compounds, or nanoparticles of metal or metaloxide, resulting in the selective placement of catalytic sites forforming nanomaterials, e.g., carbon nanotubes or semiconductornanowires.

The invention is directed to a method of forming carbon nanomaterials orsemiconductor nanomaterials. The method comprises providing a substrateand attaching a molecular precursor to the substrate. The molecularprecursor includes a surface binding group for attachment to thesubstrate and a binding group for attachment of metal-containingspecies. The metal-containing species is selected from a metal cation,metal compound, or metal or metal-oxide nanoparticle to form ametallized molecular precursor. The metallized molecular precursor isthen heated to provide a catalytic site from which the carbon orsemiconductor nanomaterials form. The heating of the metallizedmolecular precursor is conducted under conditions suitable for chemicalvapor deposition of the carbon or semiconductor nanomaterials.

The substrate can be a patterned metal, a patterned metal oxide or apatterned dielectric.

The surface binding group is selected from a thiol, an isocyanide, anorganic acid, a silane or a diene. If the substrate comprises silicon,the surface binding group will typically be a diene or if the substratecomprises silicon oxide the surface binding group will typically be achloro or alkoxy silane. If the substrate comprises metal orsemiconductors, the surface binding group will typically be a thiol orisocyanide. If the substrate comprises a metal oxide, the surfacebinding group will typically be an organic acid.

In one embodiment, the surface binding group is a thiol and thesubstrate comprises one or more metals selected from the groupconsisting of gold, palladium, platinum and copper. In anotherembodiment, the surface binding group is a thiol and the substrate is asemiconductor material selected from silicon, germanium or galliumarsenide.

The binding group for attachment of metal-containing species willtypically include a nitrogen heterocycle, an organic acid, a thiol or anisocyanide. These ligand functional groups are used to complex with avariety of metal-containing species selected from a metal cation, ametal compound or a metal or metal oxide nanoparticle. Themetal-containing species will likely contain a metal selected from thegroup consisting of iron, cobalt, nickel, palladium, platinum, rhodium,ruthenium, titanium, zirconium and gold.

The method of the invention can also include attaching a coordinatingorganic ligand to the metallized molecular precursor and attachingadditional metal-containing species to the coordinated organic ligand.

The molecular precursor used in the method of the invention can alsoinclude a photosensitive group that is displaced from the binding groupfor attachment of metal-containing species upon exposure to radiation.The removal of the photosensitive group activates the molecularprecursor to a metal-containing species selected from a metal cation, ametal compound or a metal or metal oxide nanoparticle.

The molecular precursor used in the method of the invention can alsoinclude a body portion disposed between the surface binding group andthe binding group for attachment of metal-containing species. The bodyportion can provide a sufficient intermolecular interaction withneighboring attached molecular precursors to form a molecular monolayer.Moreover, the body portion can also include a photosensitive group thatcauses the displacement of the binding group for attachment ofmetal-containing species. The removal of the photosensitive groupdeactivates the molecular precursor to metallization.

The method of the invention can be used to make a transistor. In oneembodiment, the method comprises providing a first electrode and asecond electrode on a gate dielectric or a substrate, and attaching amolecular precursor to the first electrode, the second electrode or boththe first and the second electrodes. The molecular precursor includes asurface binding group for attachment to at least one electrode and abinding group for attachment of metal-containing species. Themetal-containing species is selected from a metal cation, metalcompound, or metal or metal-oxide nanoparticle to form a metallizedmolecular precursor. The metallized molecular precursor is then heatedto provide a catalytic site from which the carbon or semiconductornanomaterials form. The heating of the metallized molecular precursor isconducted under conditions suitable for chemical vapor deposition of thecarbon or semiconductor nanomaterials.

The method can also include providing a lithographic channel between thefirst and the second electrode to allow the carbon nanomaterials orsemiconductor nanomaterials to form substantially between the twoelectrodes.

In one embodiment, the first electrode and the second electrode aredifferent materials such that the molecular precursor attachessubstantially to the first electrode with little, if any, attachment tothe second electrode. As a result, the complexing of themetal-containing species occurs predominately at the binding group formetal attachment associated with the molecular precursor that becomesattached to the first electrode.

In another embodiment, the first electrode and the second electrode arecapped with a non-reactive layer such that the molecular precursorattaches substantially at the sidewalls of the electrodes. Followingcomplexation and heating, the formed carbon nanomaterials orsemiconductor nanomaterials form along the surface of the gatedielectric.

The invention is also directed to a method of making a transistor inwhich the nanomaterials formed by the method are suspended above thegate dielectric or substrate surface (might later underfill withdielectric). The method comprises providing at least two segments of anon-reactive layer on a gate dielectric or substrate, and providing afirst electrode and a second electrode on each of the at least twonon-reactive layers. The molecular precursors are then attached to thefirst electrode, the second electrode or both the first and the secondelectrodes. The molecular precursor includes a surface binding group forattachment to at least one electrode and a binding group for attachmentof metal-containing species. The metal-containing species is selectedfrom a metal cation, metal compound, or metal or metal-oxidenanoparticle to form a metallized molecular precursor. The metallizedmolecular precursor is then heated to provide a catalytic site fromwhich the carbon or semiconductor nanomaterials form. The heating of themetallized molecular precursor is conducted under conditions suitablefor chemical vapor deposition of the carbon or semiconductornanomaterials.

The first electrode and the second electrode can comprise differentmaterials such that the molecular precursor attaches substantially tothe first electrode with little, if any, attachment to the secondelectrode. As a result, the complexing of the metal-containing speciesoccurs predominately at the binding group for metal attachmentassociated with the molecular precursor that becomes attached to thefirst electrode. In certain instances, it may be advantages to limitgrowth to the sides of the electrodes. In such a case, the firstelectrode and the second electrode are capped with a non-reactive layersuch that the molecular precursor attaches substantially at thesidewalls of at least one of the electrodes.

The inventive process can provide several advantages over the making ofelectronic devices. Some of these advantages include:

(a) the positioning of the carbon or semiconductor nanomaterials can becontrolled by the device geometry and the attachment chemistry betweenthe device surfaces (e.g., dielectric materials, metals or metal oxides,and semiconductor materials) and the surface binding groups of themolecular precursors;

(b) carbon or semiconductor nanomaterials can be selectively positionedin lithographic channels along the interface with the gate dielectric,e.g., as in field effect transistors without the typical problemsassociated with the positioning and handling of preformed carbon orsemiconductor nanomaterials;

(c) the size and density of the carbon or semiconductor nanomaterialsthat form can be controlled by selecting the type and density of thecatalytic sites; and

(d) the overlap between the substrate and the carbon or semiconductornanomaterial may be the same from device-to-device, reducing variabilityin device-to-device on-current, and potentially provide more directcontact with source and drain electrodes.

With respect to point (b), the inventive process eliminates the need forseparate growth and placement processes and overcomes the unsolvedproblem of positioning large numbers of carbon or semiconductornanomaterials in devices. Also, the inventive process avoids thepotentially harmful exposure of harvested nanomaterials to furtherprocessing. In addition, the inventive process can be combined withknown lithographic approaches to semiconductor processing.

In particular, the inventive process can be used in combination with aphotosensitive molecular precursor as described in copending U.S. patentapplication, entitled, “Photosensitive self-assembled monolayers anduses thereof”, filed on the same date as this application and assignedto International Business Machines, the entire disclosure of which isincorporated herein by reference. As described therein, thephotosensitive molecular precursors can function as a negative orpositive resist depending upon the photosensitive functionality presentin the molecule.

In one embodiment, the photosensitive functional group selectivelycleaves the molecular precursor (displacing the binding group forattachment of metal-containing species) upon exposure to radiation.Consequently, the exposed molecular precursor can no longer bemetallized, and thereby functions as a negative resist.

In another embodiment, the photosensitive functional group is displacedupon exposure to radiation. Consequently, the binding group forattachment of metal-containing species that is exposed to the radiationis activated toward metallization, thereby functioning as a positiveresist.

Compounds A, B, C and D are some examples of many different types ofphotosensitive molecular precursors that can be used n the process. Eachof the compounds have a surface binding group; A, Si(OCH₃)₃; B, PO(OH)₂;C, thiol; and D, hydroxamic acid. Each of the compounds have a metalbinding group; A, PO(OH)₂; B, pyridine; C, terpyridine; and D, S(O)₂OH.Each of the compounds have a photosensitive group; A, nitrobenzyl; B,benzyl ether; C, carbon-sulfur bond; and D, succinimidyl. Compounds Band C have internal photosensitive groups, and therefore, the bindinggroup for attachment of metal-containing species is displaced uponexposure. Compounds A and D have external photosensitive groups, andtherefore, the binding group for attachment of metal-containing speciesis activated upon exposure.

Again, it is to be understood that one of ordinary skill in the art candesign any number of photosensitive molecular precursors with eachprecursor having a surface binding group, a binding group for attachmentof metal-containing species and a photosensitive group. Accordingly,compounds A to D are only exemplary, and thus, the process is notrestricted to these four compounds. For example, a particularphotosensitive molecular precursor can be designed according to thedevice application and the type of radiation exposure.

Self-assembled monolayers (SAMs) can be formed on a given substrate fromsolution or the gas phase. The chemical interaction between specificsurface binding groups of the molecular precursors and a specificsubstrate (dielectric, semiconductor, or metal surfaces) provides theneeded control for the selective self-assembly of a precursor on aparticular surface. Some of the known surface binding groups thatself-assemble on surfaces include thiols and isocyanides on the noblemetals (platinum, palladium, and gold) and semiconductors; dienes onsilicon, chloro- and alkoxy-silanes on silicon oxide; and carboxylicacids, hydroxamic acids, and phosphonic acids on metal oxide surfacesSee, A. Ulman, Chem. Rev. 96, 1533 (1996). An organic acid is anoxygen-containing acid that is capable of binding to a metal oxidesurface, e.g., alumina, zirconia or hafnia. Exemplary organic acidsinclude phosphonic acids, hydroxamic acids, carboxylic acids andsuflonic acids.

The binding group for attachment of metal-containing species is used tobind a metal-containing species that will eventually provide catalyticsites for the growth of the carbon or semiconductor nanomaterials. Thesemetal-containing species are selected from metal cations, metalcompounds, and metal and metal oxide nanoparticles.

In one embodiment, the process uses a layer-by-layer assembly toincrease the metal content, and therefore the density or size ofcatalytic sites for carbon or semiconductor nanomaterials formation. Forexample, the careful selection as to the size and composition (e.g., theamount of metal in metal oxide nanoparticles) of the nanoparticles candirectly affect the size of both carbon nanotubes and semiconductornanowires. Examples of metal-containing species that can be formed intomultilayers include:

-   -   (a) metal ions coordinated to terpyridine, phosphonic acid [L.        Brousseau and T. Mallouk, Anal Chem. 69, 679 (1997)], and        carboxylic acid [M. Anderson, et. al. J. Vac. Sci. Technol. B        21, 3116, (2003)] functionalized organic ligands;    -   (b) metal complexes that include one or more pyridine, or        isocyanide, ligands [C. Lin, C. R. Kagan, J. Am. Chem. Soc. 125,        336 (2002), M Ansell et. al. Langmuir 16, 1172 (2000), and C. R.        Kagan, C. Lin, see U.S. Pat. No. 6,646,285.]; and    -   (c) metal nanoparticles, e.g., gold nanoparticles on thiol        functionalized molecules, and iron-platinum particles on        polyvinylpyrrolidinone [S. Sun et. al. J Am Chem. Soc. 124, 2884        (2002)].

Following the metallization of the attached molecular precursors, thedevice structure is exposed to known reaction conditions for makingnanomaterials, e.g., carbon nanotubes or semiconductor nanowires. Thebound metal-containing species provide the necessary catalytic sites forthe growth of the nanomaterials as the molecular precursor volatilizesat the elevated temperatures necessary for forming the carbonnanomaterials or semiconductor nanomaterials.

FIGS. 1( a) to 1(f) is a schematic representation of one embodiment ofthe process. FIG. 1( a) depicts a field-effect transistor with gate 14,gate dielectric 12, and metal source or drain electrodes 10. Theself-assembly of the selected molecular precursors, which are attachedto the electrodes by the surface binding groups, is depicted in FIG. 1(b). As shown, the molecular precursor 20 includes a surface bindinggroup (square, 22) that selectively binds to a metal, semiconductor, ordielectric surface. Such surface binding groups include:

a. thiols that bind to metal and semiconductor surfaces (e.g. Au, Pd,Pt, AuPd, Si, Ge, GaAs, Cu);

b. isocyanides that bind to metal surfaces;

c. phosphonic acids, hydroxamic acids, carboxylic acids, suflonic acidsthat to bind to metal oxide surfaces (e.g. alumina, zirconia, hafnia);

d. silanes that bind to silicon oxide surfaces; and

e. dienes that bind to silicon surfaces.

As shown, the molecular precursor 20 also includes a body (oval, 24)which can in some instances, facilitate the self assembly of themolecular precursor on the substrate. For example, Π-stacking orhydrogen bonding between neighboring precursors can have a dramaticaffect on the arrangement of molecules in the monolayer throughintermolecular interactions. The body portion can, for instance, containaromatic groups (including phenyl rings and heterocycles, and/or alkylgroups. One can also design the body portion of the molecular precursorwith groups capable of forming hydrogen bonds.

The body 24 can also have groups that provide bulkiness to control thedensity of molecules on the surface. A more bulkier body results in asmaller number of attached precursors over a given area of substratesurface, and hence a decrease in the amount of catalyst.

As shown, the molecular precursor 20 also includes a binding group forattachment of metal-containing species (triangle, 26) that is capable ofcoordinating a metal cation, metal complex, or metal or metal-oxidenanoparticle. Such metal binding groups include:

a. nitrogen heterocyclic ligands e.g., pyridine, bipyridine andterpyridine which bind Fe, Co Ru, Ti, Zr, Mo and W ions, complexes, ornanoparticles;

b. sulfonic acids which coordinate Fe;

c. thiols which coordinate Au, Pd, Pt; and

d. isocyanides which coordinate Au, Pd, Pt;

e. amines which bind metal oxide nanoparticles

Once attachment of the precursor to the surface is completed, theprecursor is bound by attaching a metal cation, metal complex, or metalor metal-oxide nanoparticle to the metal binding group, FIG. 1( c). Theattached precursors are exposed to a solution of metal cations or metalcompounds or a dispersion of metal or metal oxide nanoparticles(rectangles, 30) that coordinate to the metal binding group of theprecursor, thereby adding a layer of metal cations or metal compounds,or metal or metal oxide nanoparticles to the assembled precursors on thesubstrate surface.

Following metallization, the nanomaterials, e.g., carbon nanotubes orsemiconductor nanowires, form from the substrate surface as themolecular precursor decomposes leaving the necessary catalytic sites,FIG. 1( f). If an increase in the concentration of catalytic sites isdesired, additional coordinating ligands 40 can be attached to the metalcations, metal compounds, or metal or metal oxide nanoparticles bound tothe molecular precursors. The organic ligands may have bindingfunctionalities (circles, 42) such as pyridines, isocyanides,terpyridines, sulfonic acids, etc. that coordinate the metal ions orcomplexes, or metal or metal oxide nanoparticles both attached to thefirst layer of metal-containing species and to a subsequently depositedsecond layer of metal-containing species. This additive process can berepeated any number of times to add sufficient metal content to thesubstrate surface until the desired amount of catalyst is obtained forthe growth of the carbon nanomaterials or semiconductor nanomaterials,FIGS. 1( d) and 1(e).

Once the desired metal content is achieved, the metal containingassembly is exposed to elevated temperatures, typically under chemicalvapor deposition conditions, for the growth of the nanomaterials 50(e.g., nanotubes or nanowires), FIG. 1( f). During this process theorganic component of the molecular assembly decomposes leaving behindinorganic nanoparticles that serve as catalytic sites for the growth ofthe nanomaterials. The nanomaterials 50 grow from the catalyst sites andmay span the electrodes 10 of the device.

FIG. 2 is a schematic representation of another embodiment of theprocess. As in FIG. 1, FIG. 2 represents a field-effect transistor withgate 140, gate dielectric 120, and metal source or drain electrodes 100that are capped with a relatively non-active layer 110 to provide anelectrode stack. As shown, the molecular precursors (as shown in FIG. 1)selectively attach to only the sidewalls of electrodes 100 in theelectrode stack in a direction parallel to the gate dielectric 120. Thenon-active layer 110 can include a native oxide, which will limitdiffusion of the catalytic metal sites upon exposure to the elevatedtemperatures later in the process.

In still another embodiment, the capping layer above can be selected forattachment of the molecular precursor with the lower metal electrodebeing non-reactive toward the surface binding group of the molecularprecursor. The result of which would be the fabrication of suspendednanostructures.

The invention is also directed to a method of forming an electronicdevice structure. The method comprises providing a patterned electronicsurface selected from a patterned metal surface, a patterned dielectricsurface or a patterned semiconductor surface. A molecular precursor isthen attached to the patterned electronic surface. The molecularprecursor includes a surface binding group for attachment to thepatterned electronic surface and a binding group for attachment ofmetal-containing species. The metal-containing species is selected froma metal cation, metal compound, or metal or metal-oxide nanoparticlecomplexes, which attach to the metal binding group to form a metallizedmolecular precursor.

Alternatively, a patterned assembly of molecular precursor can be formedby exposing portions of the assembly to radiation. In this instance, themolecular precursor will include a photosensitive group. Followingselective attachment to a substrate, the assembled monolayer is exposedto radiation resulting in a patterned assembly. The patterned assemblyis then exposed to metal cations, metal compounds, or metal or metaloxide nanoparticles for selective positioning of the catalytic sites andthe resulting carbon nanomaterials or semiconductor nanomaterials.

In still another embodiment, a single metal electrode can be used as asubstrate surface, and following the formation of the nanomaterial,another electrode can be patterned on the surface to complete the devicestructure. Alternatively, the two metal electrodes forming the activeregion of the device can have different chemical reactivity towards thesurface binding group of the molecular precursor. As a result, selectiveassembly of the catalyst on and subsequent growth of the nanomaterialonly one of the electrodes in the device occurs.

While the above described embodiments depict the selective growth ofcarbon nanomaterials or semiconductor nanomaterials on electrodesurfaces, one of ordinary skill in the art would understand that thecarbon nanomaterials or semiconductor nanomaterials can be grown on apatterned metal, dielectric, or semiconductor surfaces by selectivelypositioning the molecular assembly. This could be achieved by patterningthe underlying dielectric surface with metal oxide and silicon dioxideand using a molecular precursor that assembles on only one of the twosurfaces, by using a stamp to put down a patterned monolayer, or bydepositing the molecular assembly with a lithographic mask prepared byphotolithography or using a block copolymer template.

Making the Carbon or Semiconductor Nanomaterials

There have been many studies directed to growing carbon nanotubes. Forexample, one such method is described by H. Dai, Acc. Chem. Res. 35,1035 (2002). Similarly, there have been many studies directed to growingsemiconductor nanomaterials. For example, one such method is describedby C. M. Lieber, MRS Bull. July, 286 (2003). One of ordinary skill inthe art can grow carbon nanotubes or semiconductor nanomaterials (e.g.,nanowires) using the process of positioning catalytic sites as describedin this application followed by the growth of the nanomaterials usingthe methods described in these two technical articles.

Applicants provide the following Examples, which help describe theprocess of the invention. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

EXAMPLE 1

A heavily n+ doped silicon wafer, with 10 nm thermally grown siliconoxide was patterned with electrodes consisting of 10 Å Ti followed by190 Å Pd. The patterned substrate was exposed to 1 mMmercaptoterypyridine in 50:50 toluene:ethanol for a period of 18 hrs,resulting in the assembly of mercaptoterypridine on the Pd surfaces. Thesamples were rinsed well in clean 50:50 toluene:ethanol and exposed to 5mM Fecl₃ in ethanol for a similar period of 18 hrs. The samples wererinsed in clean ethanol and dried under a nitrogen stream.

EXAMPLE 2

A heavily n+ doped silicon wafer, with 10 nm thermally grown siliconoxide was patterned with electrodes consisting of 10 Å Ti followed by190 Å Pd. The patterned substrate was exposed to 1 mMmercaptoterypyridine in 50:50 toluene:ethanol for a period of 18 hrs,resulting in the assembly of mercaptoterypridine on the Pd surfaces. Thesamples were rinsed well in clean 50:50 toluene:ethanol and exposed todispersion of iron oxide nanoparticles in hexane for a period of 18 hrs.The samples were rinsed in clean hexane and dried under a nitrogenstream.

EXAMPLE 3

A heavily n+ doped silicon wafer, with 10 nm thermally grown siliconoxide was patterned with electrodes consisting of 10 Å Ti followed by190 Å Pd. The patterned substrate was exposed to 1 mM aminoethanethiolin ethanol for 18 hrs, resulting in the assembly of aminoethanethiol onthe Pd surfaces. The samples were rinsed well with clean ethanol andexposed to a dispersion of iron oxide nanoparticles in hexane for aperiod of 18 hrs. The samples were rinsed in clean hexane and driedunder a nitrogen stream.

EXAMPLE 4

A heavily n+ doped silicon wafer with 10 nm thermally grown siliconoxide was pattered with an electrode stack consisting of 10 Å Ti, 50 ÅPd, and 140 Å Al. The pattered substrate was exposed to 1 mMmercaptoterpyridine in 50:50 toluene:ethanol for a period of 18 hrs. TheTi and Al surfaces form a native surface oxide that is subsequentlynon-reactive towards mercaptoterpyridine, resulting in the selectiveassembly of mercaptoterpyridine on the exposed Pd sidewalls of the metalstack. The samples were rinsed well in clean 50:50 toluene:ethanol andexposed to 5 mM Fecl₃ in ethanol for a period of 18 hrs. The sampleswere rinsed in clean ethanol and dried under a nitrogen stream.

EXAMPLE 5

A heavily n+ doped silicon wafer with 10 nm thermally grown siliconoxide was pattered with an electrode stack consisting of 10 Å Ti, 50 ÅPd, and 140 Å Al. The pattered substrate was exposed to 1 mMaminoethanethiol in ethanol for a period of 18 hrs. The Ti and Alsurfaces form a native surface oxide that is subsequently non-reactivetowards aminoethanethiol, resulting in the selective assembly ofaminoethanethiol on the exposed Pd sidewalls of the metal stack. Thesamples were rinsed well in clean ethanol and exposed to a dispersion ofiron oxide nanoparticles in hexane for a period of 18 hrs. The sampleswere rinsed in clean hexane and dried under a nitrogen stream.

EXAMPLE 6

Each of the deposited structures of Examples 1-5 were placed on a quartzboat in a 1-inch diameter quartz tube reactor for CVD growth of carbonnanotubes. The tube reactor was heated to 870° C. under a flow of 5% H₂in Ar (rate˜2700 sccm). The carbon nanotubes were formed by bubbling a5% H₂ in Ar gas mixture through a bottle of ethanol, cooled to 0° C.,and flowing it over the samples at 870° C. for 7 minutes. The reactorwas then allowed to cool to room temperature under flowing Ar.

FIG. 3 is a scanning electron micrograph of grown carbon nanotubes usingthe deposited catalytic sites of Fecl₃ of Example 1. Likewise, FIG. 4 isa scanning electron micrograph of grown carbon nanotubes using thedeposited catalytic sites of Fecl₃ of Example 4. In the capped electrodeof Example 4, the total number of grown nanotubes was greatly reduced asthe catalytic sites were limited to the Pd sidewall.

The foregoing description illustrates and describes the presentdisclosure. Additionally, the disclosure shows and describes only thepreferred embodiments of the disclosure, but, as mentioned above, it isto be understood that it is capable of changes or modifications withinthe scope of the concept as expressed herein, commensurate with theabove teachings and/or the skill or knowledge of the relevant art.Accordingly, the description is not intended to limit the invention tothe form disclosed herein.

1. A method of forming carbon nanomaterials or semiconductornanomaterials consisting of: providing a substrate and attaching amolecular precursor to the substrate, wherein the molecular precursorincludes a surface binding group for attachment to the substrate and abinding group for attachment of metal-containing species; complexing thebinding group for attachment of metal-containing species, where themetal-containing species is a metal-oxide nanoparticle to form ametallized molecular precursor; and heating the metallized molecularprecursor to provide a catalytic site from which the carbonnanomaterials or semiconductor nanomaterials form wherein the molecularprecursor further consists of a body portion disposed between thesurface binding group and the binding group for attachment ofmetal-containing species, wherein the body portion provides a sufficientintermolecular interaction with neighboring attached molecularprecursors to form a molecular monolayer, wherein the surface bindinggroup is a thiol and the substrate is gold and wherein the metal oxidenanoparticle contains iron.